However, after related studies, it is shown that the corrected law still cannot explain all the anomalies well. In 2014, Xie et al pointed out that due to the periodicity of the metasurface structure, higher-order diffraction occurs when the incident wave is larger than a certain critical angle, and the transmission angle no longer satisfies the GSL, and the higher-order diffraction term needs to be introduced to correct the law. Since then, a large number of studies have emerged on the use of metasurfaces to modulate the phase of acoustic waves. In 2013, Li et al extended GSL from optics to acoustics and designed a spatially folded metasurface to discretize the phase gradient to achieve anomalous reflection and acoustic focusing. The proposed GSL shows that it is possible to introduce the phase mutation through a two-dimensional interface, and thus a series of anomalous acoustic phenomena such as negative refraction and acoustic focusing can be realized more easily and conveniently. In 2011, Yu et al introduced phase mutation at the interface through a periodic array of V-shaped antennas to reach the modulation of the phase of the incident light wave and further realize the anomalous reflection and transmission of the wave, and the reflection and transmission angles satisfy the so-called Generalized Snell’s Law (GSL). With the depth of research, the regulation of elastic waves has gradually become the focus of attention, and the emergence of metasurface structures in recent years is one of the means to effectively regulate elastic waves. Finally, the asymmetric transmission, modal separation and waveguide of Lamb waves in thin plates are realized by combining the theory with structural design, which proves that the structure has great application potential in ultrasonic detection and other fields.Įlastic waves are a classical form of motion in engineering structures, and the mechanical vibrations of major equipment such as aerospace vehicles, underwater probes, and high-speed trains are essentially the superimposed effects of their internal elastic waves. In order to verify whether the modified GSL theory considering the higher-order diffraction term is still applicable to the regulation of solid elastic waves, this paper designs a helical metasurface based on the elastic wave theory of plate-beam structure, which is composed of helical lines of different lengths, and uses this structure to explain the complex transmission phenomenon of elastic wave metasurface. Under the action of higher order diffraction wave, the incident wave will produce more complex transmission phenomenon when passing through the metasurface, and the angle of transmission does not conform to GSL in some cases. However, most of the researches on elastic wave metasurface are guided by traditional Generalized Snell’s Law (GSL), and the effect of higher order diffraction waves caused by structural periodicity is not considered. Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang, ChinaĪs a new kind of elastic materials, elastic wave metasurface has great research significance in the field of elastic wave regulation.
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